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osmolarity

http://www.youtube.com/watch?v=qRuNxHqwazs

drink water. whether you feel you want/need it or not. especially if working long hours in hot conditions or any workout over 30 minutes. it's really not that hard a question. :)

imo, it depends upon your average hydration.

if you normally stay well hydrated then you could do an hour workout w/o hydrating.

if you aren't normally well hydrated (check your ****, average...